The invention relates to a boiler having a fire chamber which is cooled by water, and a door which is likewise cooled by water, in which an opening for an oil or gas burner is located. A boiler possessing these features is described in DE 40 16 880 A1. Here the entire fire chamber is cooled by water circulating in an annular wall surrounding the cylinder of the chamber and in the front door and rear face wall.
A warm-water boiler having a fire chamber rinsed by water is described in DE-AS 1 579 940. This boiler includes a hollow rotating body whose diameter increases toward the end of the fire chamber where the door is located. A diffuser-type configuration of the cooling device is achieved, with the additional advantage of reducing noise by attaining a laminar flow of the heating gases. The heating surfaces of this boiler are also intended to be acted upon uniformly by the fuel gases, increasing the efficiency of the boiler. A steam boiler whose one face will have a double-cone-shaped insert, and whose double wall has boiler water flowing therethrough, is described in DE-U-1 911 608. In this design, the cross-section of the insert tapers toward the interior of the boiler, making it inappropriate for oil or gas fired boilers.
U.S. Pat. No. 5,611,299 discloses a water-cooled boiler door with water pumped in and out of the top portion of the door. Such a configuration works for hot water boilers, but not for steam boilers because it does not provide an exit path for the steam.
U.S. Pat. No. 5,168,818 discloses a liquid cooled boiler door in which liquid enters the bottom of the door and flows out through the top. This door is designed to function as a water cooled turnaround chamber in a dryback Scotch Marine type boiler, and cannot accommodate attachment of a burner to the inside of the door. Moreover, the hemispherical shape needed for effective functioning of the disclosed door adds substantially to the overall length, and when opened also to the width of the boiler, which is undesirable in most boiler applications.